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Radio-frequency interference detection and flagging is one of the most difficult and urgent problems in 21 cm Epoch of Reionisation research. In this work, we present χ2 from redundant calibration as a novel method for RFI detection and flagging, demonstrating it to be complementary to current state-of-the-art flagging algorithms. Beginning with a brief overview of redundant calibration and the meaning of the χ2 metric, we demonstrate a two-step RFI flagging algorithm which uses the values of this metric to detect faint RFI. We find that roughly 27.4% of observations have RFI from digital television channel 7 detected by at least one algorithm of the three tested: 18.0% of observations are flagged by the novel χ2 algorithm, 16.5% are flagged by SSINS, and 6.8% are flagged by AOFlagger (there is significant overlap in these percentages). Of the 27.4% of observations with detected DTV channel 7 RFI, 37.1% (10.2% of the total observations) are detected by χ2 alone, and not by either SSINS or AOFlagger, demonstrating a significant population of as-yet undetected RFI. We find that χ2 is able to detect RFI events which remain undetectable to SSINS and AOFlagger, especially in the domain of long-duration, weak RFI from digital television. We also discuss the shortcomings of this approach and discuss examples of RFI which seems undetectable using χ2 while being successfully flagged by SSINS and/or AOFlagger.